APPLICATION OF A PLANAR ENZYME MICROELECTRODE TO BIOPROCESS MONITORING

Abstract

Using microelectronic technology it has been possible to develop disposable glucose electrodes (1). The transducer is realised using thin-film deposition and lift-off techniques, and consists of two Pt electrodes (working and counter) and an Ag/AgCl reference electrode. This transducer is covered with an enzyme membrane. The hydrogen peroxide formed by the enzyme catalysed reaction is measured at + 0.6 V. For use in FIA, such electrodes must meet certain specifications as to response time, sensitivity, reproducibility, accuracy, and electrode lifetime. We have investigated the performance of electrodes in an FIA system with particular reference to the measurement of glucose at low concentration in culture media. Typical performance characteristics are - a) a lifetime of 14 days b) a sensitivity ( peak height ) of 30 yA M-1 at a flow rate of 1.4 ml min"! and sample volume of 190 ul c) anoise level below 5 pA d) a linear response from 1.0 HM to 1 mM glucose The detection limit is determined not by the signal / noise ratio, but by the presence of interfering compounds within the sample. We have determined quantitatively the level of this interference during mammalian cell culture, and have shown it to be much smaller than expected. It is possible to include additional membrane layers in construction of the sensor. These would be designed to reduce such interference and thus increase specificity. Our results suggestthat this may not be necessary.